1. Field of the Invention
The present invention relates to an actuator with a quick release capability.
2. The Prior Art
For the sake of convenience, the description of the invention departs from linear actuators of the type comprising a spindle, which over a gearing, is driven by an electric motor, and where the activation element is a tubular rod carried by a spindle nut. It is, however, to be understood that the invention also applies to rotary actuators for instance of the type dealt with in WO 01/17401 A1 to Linak A/S
A quick release in an actuator is used for temporary interruption of the connection to the part of transmission with a high inertia and motor so that the activation element, which is of the non-self-locking type, under its load on its own momentary moves back to its initial position, alternatively can be adjusted manually. As an example of where a quick release is used, reference is made to hospital and care beds, patient lifters and certain types of gates, doors and windows and other constructions, where it is important if not vital to be able to make a momentary adjustment of the activation element.
Actuators with quick release are for instance known from EP 685 662 B1 and EP 577 541 B1 to Linak A/S. The first publication deals with a quick release based on two cylindrical elements wound with an disengageable clutch spring. The other publication deals with a quick release with two bevel gear wheels, where one gear wheel can be displaced out of engagement.
By quick releases there is, however, in many situations a risk that the construction, the load and the possible patient carried by the actuator may be damaged as a result of the collision-like impact which occurs when the activation element hits a mechanical end stop in the end position. That the collision is intense is due to the fact that the activation element under influence of the load executes an accelerated movement and typically into a more or less rigid mechanical stop.
A simple structure is, however, known from WO 98/30816 to Linak A/S, where the velocity can be controlled during the release of the quick release. This quick release is based on a clutch spring in the form of a coil spring, which rests tightly against a cylindrical element. By releasing the spring in a controlled manner it can be achieved that it is brought more or less out of engagement with the cylindrical element and thus controlling the velocity. The construction is as far as it goes fine, but it is voluminous, and has several components, and it can be difficult to control the velocity accurately.
The purpose of the invention is to provide an actuator with a simplified quick release with controlling of the velocity during the disengagement.